1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating the same, and more particularly, to a color filter substrate for an LCD device and a method of fabricating the same.
2. Discussion of the Related Art
A liquid crystal display (LCD) device is driven based on the optical anisotropy and birefringence characteristics of a liquid crystal material to display images. In general, the LCD device includes two substrates that are spaced apart and face each other, and a liquid crystal material layer interposed between the two substrates. Each of the substrates includes electrodes that face each other, wherein a voltage applied to each electrode induces an electric field perpendicular to the substrates between the electrodes. An alignment of liquid crystal molecules of the liquid crystal material layer changes by varying an intensity or direction of the applied electric field. Accordingly, the LCD device displays an image by varying light transmittance through the liquid crystal material layer in accordance with the arrangement of the liquid crystal molecules.
FIG. 1 is an expanded perspective view illustrating the related art LCD device. As shown in FIG. 1, the LCD device 11 includes an upper substrate 5, referred to as a color filter substrate, and a lower substrate 22, referred to as an array substrate, having a liquid crystal material layer 14 interposed therebetween. On an inner surface of the upper substrate 5, a black matrix 6 and a color filter layer 8 are formed as an array matrix including a plurality of red (R), green (G), and blue (B) color filters surrounded by corresponding portions of the black matrix 6. Additionally, a common electrode 18 is formed on the upper substrate 5 to cover the color filter layer 8 and the black matrix 6.
On an inner surface of the lower substrate 22, a plurality of thin film transistors (TFTs) T are formed in the array matrix corresponding to the color filter layer 8. A plurality of gate lines 13 perpendicularly cross a plurality of data lines 15. The TFTs T are positioned such that each TFT T is located adjacent to an intersection of one of the gate lines 13 and one of the data lines 15. Furthermore, a pixel electrode 17 is formed on each of pixel regions P defined by the gate lines 13 and the data lines 15 of the lower substrate 22. The pixel electrode 17 includes a transparent conductive material having high transmittance, such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).
As further shown in FIG. 1, a storage capacitor CST is disposed in each pixel and connected in parallel to the pixel electrode 17 of the pixel. The storage capacitor CST includes a portion of the gate line 13 as a first capacitor electrode and a metal layer 30 as a second capacitor electrode. Since the metal layer 30 is connected to the pixel electrode 17 through a contact hole, the storage capacitor CST is electrically connected to the pixel electrode 17. The metal layer 30 may be made of the same material as the data line 15.
In the LCD device, a pixel is composed of three sub-pixels of red, green and blue. To improve brightness of the LCD device, a quad type LCD device, in which a pixel is composed of four sub-pixels of red, green, blue and white, has been suggested and been developed.
FIG. 2 is a cross-sectional view of a color filter substrate for an LCD device including red, green, blue and white sub-pixels according to the related art. In FIG. 2, a black matrix 120 having openings 125 is formed on a substrate 110. A color filter layer 130 is formed on the substrate 110 and corresponds to the openings 125 of the black matrix 120. An overcoat layer 140 is formed on the color filter layer 130, and a column spacer 150 is formed on the overcoat layer 140.
The black matrix 120 is formed of a light-blocking material and corresponds to gate lines, data lines and thin film transistors, which are formed on an array substrate facing the color filter substrate. Because liquid crystal molecules adjacent to the gate lines, data lines and the thin film transistors may be abnormally driven so as to cause light leakage, the black matrix blocks the light leakage. The black matrix 120 has first, second, third and fourth openings 125a, 125b, 125c and 125d for each pixel.
The color filter layer 130 includes red, green and blue color filters 130a, 130b and 130c, which are made of photosensitive materials for displaying red, green and blue colors, respectively. The red, green and blue color filters 130a, 130b and 130c correspond to the first, second and third openings 125a, 125b and 125c, respectively. There is no color filter corresponding to the fourth opening 125d. 
The overcoat layer 140 serves as a planarization layer for flattening a surface of the substrate 110 including the color filter layer 130. The overcoat layer 140 is formed of a transparent organic material, for example, an acrylic material. The overcoat layer 140 covers the color filter layer 130 and fills the fourth opening 125d. Since there is no color filter corresponding to the fourth opening 125d, the overcoat layer 140 has a hollowed portion in a region corresponding to the fourth opening 125d. 
A column spacer 150 is formed on the overcoat layer 140. The column spacer 150 maintains a cell gap between the color filter substrate and an array substrate, which are spaced apart from each other and face each other. The cell gap is filled with a liquid crystal material. Thus, the column spacer 150 determines the thickness of the liquid crystal layer between a top surface of the overcoat layer of the color filter substrate and a top surface of the array substrate.
The color filter substrate may be manufactured through processes of forming the black matrix on the substrate, forming the color filter layer of red, green and blue color filters, forming the overcoat layer, and forming the column spacer. There is a problem is that a surface of the overcoat layer is uneven because there is no color filter in the region for a white sub-pixel. Thus, the thickness of the liquid crystal layer or the cell will be varied.
FIG. 3 is a cross-sectional view of another color filter substrate according to the related art. In FIG. 3, red, green, blue and white color filters 230a, 230b, 230c and 230d are formed on a substrate 210 and corresponds to first, second, third and fourth openings 225a, 225b, 225c and 225d of a black matrix 220. The white color filter 230d is substantially formed of a transparent material and transmits white light therethrough. The red, green, blue and white color filters 230a, 230b, 230c and 230d may have substantially the same thickness. An overcoat layer 240 is formed on the red, green, blue and white color filters 230a, 230b, 230c and 230d, and a column spacer 250 is formed on the overcoat layer 240. Accordingly, the overcoat layer 240 has an even surface such that the cell gap will be uniform or a subsequently formed liquid crystal layer will have a uniform thickness. However, a process for forming the white color filter is added, and thus the color filter substrate of FIG. 3 is manufactured through more processes than the color filter substrate of FIG. 2.